白英果提取物清除DPPH自由基活性研究

确定了以分光光度法测定天然抗氧化剂清除2,2-Diphenyl-1-picrylhydrazyl（2，2-二苯基-1-苦肼基，DPPH）自由基能力的条件。通过测定芦丁、槲皮素、抗坏血酸、没食子酸的自由基清除率曲线，提出以IC50值作为评价试样清除DPPH自由基能力的指标，并将此应用于白英果提取物清除DPPH自由基能力的测定，测得白英果乙醇提取液、乙酸乙酯提取液以固形物计算的IC50值分别为0．230和1．010。     

Effects of Trolox and ascorbic acid on the riboflavin photosensitised oxidation of aromatic amino acids

The effects of 0, 100, 250, 500, 750 or 1000 ppm Trolox and ascorbic acid on the singlet oxygen oxidation of aromatic amino acids viz. phenylalanine, tryptophan, tyrosine in the presence of 25 ppm riboflavin were determined by measuring depleted headspace oxygen by gas chromatography and aromatic amino acid content by high performance liquid chromatography. The coefficients of variations (CVs) for headspace oxygen analysis and HPLC analysis of aromatic amino acids were 1.4% and 4.7%, respectively. Samples were stored under light (1000 lux) at 30 °C for 10 h. Both Trolox and ascorbic acid acted as antioxidants. As the concentration of Trolox and ascorbic increased from 0 to 1000 ppm, the head space oxygen depletion increased. This was due to the oxidation of Trolox and ascorbic acid along with amino acids in the presence of riboflavin. High performance liquid chromatography analysis of the samples clearly indicated that both Trolox and ascorbic acid minimised the degradation of phenylalanine, tryptophan, tyrosine significantly (p < 0.05), but did not prevent their oxidation completely. Trolox acted as a better antioxidant than ascorbic acid in protecting phenylalanine, tryptophan and tyrosine. Type-I mechanism was mainly responsible for riboflavin photosensitised degradation of aromatic amino acids.     

A reappraisal of traditional apple cultivars from Southern Italy as a rich source of phenols with superior antioxidant activity

Few literature data are available on the nutraceutical properties of little widespread local apple cultivars. Such lack of information prevents exploitation of these germplasms for genetic improvement of new cultivars and for the re-evaluation of local agricultural products, which may attract a large share of consumers oriented towards natural food evoking ancient flavours. In this work eight traditional apple cultivars of Southern Italy were analysed in terms of phenolic composition and free radical scavenging activity in comparison with commercial “Annurca” and “Gold Chief® Gold Pink∗” cultivars. HPLC-UV-MS analysis of methanol extracts of the cultivars under examination showed significant differences in phenol distribution within the three main classes of hydroxycinnamates, dihydrochalcones, and flavan-3-ols. Such differences were found to be associated with the antioxidant activities as determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. A good correlation was observed between the percentage of reduced DPPH and the total phenol content (R = 0.79). Among all phenol classes, the flavan-3-ol content showed the highest correlation (R = 0.77). Almost all of the traditional cultivars examined exhibited a much higher phenol content (2- to 7-fold) and hydrogen donor activity (1.5- to 4-fold) than widely consumed cultivars like “Annurca” and “Gold Chief® Gold Pink∗”.     

高效液相色谱法测定葡萄酒的有机酸及乙酸

采用高效液相色谱法同时测定葡萄酒中的有机酸和乙酸。根据色谱柱的特点优化了分离条件，根据葡萄酒的特性进行了相应的预处理，得出了分离良好的色谱图，各组分相对标准偏差（n=5）为1．5％－3．3％，平均回收率为93．9％－98．5％，达到了分析方法的要求。     

Effect of pasteurisation on ascorbic acid,dehydroascorbic acid,tocopherols and fatty acids in pooled mature human milk

Ascorbic and dehydroascorbic acids (vitamin C), tocopherols (vitamin E) and unsaturated fatty acids are heat-sensitive and therefore, their concentrations in human milk could be affected by pasteurisation. Here we determined the concentrations of ascorbic acid plus dehydroascorbic acid, ascorbic acid alone, and α- and γ-tocopherols, and the percentages of fatty acids in samples of human milk after pasteurisation by a slow (62.5 °C, 30 min) or fast heating (100 °C, 5 min) procedure. Both methods led to a significant decrease in the concentrations of ascorbic acid plus dehydroascorbic acid (12% and 29%), ascorbic acid (26% and 41%), α-tocopherol (17% and 34%) and γ-tocopherol (13% and 32%), respectively. However, milk fatty acids, including the polyunsaturated long-chain fatty acids, were unaffected by the two methods. On the basis of these observations, we recommend that human milk be treated using a slow pasteurisation. In addition, we propose ascorbic acid as a marker of the degree of heat treatment.     

植物精油气相清除DPPH自由基的研究

采用分光光度法研究了12种植物精油在气相状态下清除DPPH自由基的能力。实验结果显示丁香精油、肉桂精油、茶树油和甘牛至油清除自由基的效果较好,其中丁香精油最好,其次是肉桂精油;延长反应时间、升高反应温度、提高空间精油浓度能有效促进精油对自由基的清除效果。植物精油中的抗自由基活性成分是其清除自由基的关键,高抗自由基活性成分含量越高,其清除自由基的效果也越好;活性成分的挥发性是影响精油气相清除自由基效果的另一个重要因素,高挥发性可使空间精油浓度较高,精油气相清除自由基的效率也就提高。     

Formation of pyrazines from ascorbic acid and amino acids under dry-roasting conditions

Although the participation of ascorbic acid in Maillard-type reactions has been described, the formation of flavour compounds resulting from the interaction of ascorbic acid with different amino acids has not been reported before. Therefore, the formation of flavour compounds from the model reactions of 20 amino acids with ascorbic acid was studied under dry-roasting conditions. Thirty-six different pyrazines were identified, mostly ethyl and methyl substituted pyrazines. The amounts of pyrazines detected were comparable to those formed from pentose sugars. Lysine was the most reactive amino acid and yielded the highest amounts of alkylpyrazines. The reducing activity of ascorbic acid influenced the reaction mechanism of pyrazine formation and thus the type of pyrazines produced. Addition of a base, such as potassium carbonate, significantly enhanced pyrazine formation from ascorbic acid for most amino acids. The formation of pyrazines from serine and threonine without a carbonyl compound was greatly enhanced by the addition of potassium carbonate as well. Furan was detected in all model systems in relatively low amounts and its formation was not enhanced by the addition of potassium carbonate.     

后发酵过程中乙醇对豆豉抗氧化能力的影响

以黄豆为原材料,接种米曲霉制作豆豉,在豆豉后发酵过程中设定了不同乙醇添加量,测定了不同乙醇添加量的豆豉样品清除DPPH(2,2-diphenyl-1-picrylhydrazyl hydrate)及ABTS[2,2-’azinobis-(3-ethylbenzthia-zoline-6-sulfonic acid)]自由基能力、Fe2+螯合能力、还原能力,评价了乙醇对豆豉抗氧化能力的影响。后发酵过程中,豆豉的抗氧化能力持续增大,醇对豆豉的抗氧化能力有影响,发酵相同时间的豆豉,抗氧化能力随乙醇含量的增大而下降。     

桔核中柠檬苦素类物质最佳提取条件的探讨及清除DPPH活性的研究

文章对桔核中柠檬苦素类物质的提取条件及其清除DPPH活性进行研究。结果表明：桔核粉碎物以85倍体积的混合溶液（A：B=55：45，其中A为极性溶剂，B为极性溶剂），温度在65℃下，提取3．5h，一次提取即达到最佳的提取效果。桔核中的柠檬苦素清除DPPH自由基的IC50值为20．7μg／mL。     

Effect of ultrasonic treatment on the recovery and DPPH radical scavenging activity of polysaccharides from longan fruit pericarp

Ultrasonic technique was employed to extract polysaccharides from longan fruit pericarp (PLFP). The optimal conditions for ultrasonic extraction of PLFP were determined by response surface methodology. Box–Behnken design was applied to evaluate the effects of three independent variables (ultrasonic power, time and temperature) on the recovery and 1,1′-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of PLFP. The correlation analysis of two mathematical-regression models indicated that quadratic polynomial model could be employed to optimize the ultrasonic extraction of PLFP. From response surface plots, ultrasonic power, time and temperature exhibited independent and interactive effects on the extraction of PLFP. The DPPH radical scavenging activity of PLFP could be improved by application of various ultrasonic power, time and temperature, which was possible due to the degradation of polysaccharides to different extent. The optimal conditions to obtain the highest recovery and the strongest DPPH radical scavenging activity of PLFP were 120 W, 22 min and 60 °C, as well as 241 W, 18 min and 51 °C, respectively. Under these optimal conditions, the experimental values agreed with the predicted ones by analysis of variance. It indicated high fitness of two models used and the success of response surface methodology for optimizing PLFP extraction.     

响应面优化虾头壳酶促水解清除DPPH自由基活性的研究

以碱性蛋白酶水解虾头壳蛋白质,在影响水解条件单因素研究基础上,采用响应面方法中心组合设计,建立以DPPH自由基清除率为指标的水解模型,优化得出最佳酶解条件,并测定水解液中多肽的相对分子质量分布。结果表明,最佳酶解条件为pH7.2、温度50.5℃、加酶量415U/g、时间120min。在此条件下水解,水解度达21.8%,DPPH自由基清除率为66.9%,平均肽段长度为4.6,酶解液中大部分肽的相对分子量低于6500u。     

Sensorially important aldehyde production from amino acids in model wine systems: Impact of ascorbic acid,erythorbic acid,glutathione and sulphur dioxide

The efficiency of different white wine antioxidant systems in preventing aldehyde production from amino acids by oxidative processes is not well understood. The aim of this study was to assess the efficiency of sulphur dioxide alone and in combination with either glutathione, ascorbic acid or its stereoisomer erythorbic acid, in preventing formation of the sensorially important compounds methional and phenylacetaldehyde from methionine and phenylalanine in model white wine. UHPLC, GC–MS/MS, LC–MS/MS, flow injection analysis and luminescence sensors determined both compositional changes during storage, and sulphur dioxide–aldehyde apparent equilibrium constants. Depending on temperature (25 or 45 °C) or extent of oxygen supply, sulphur dioxide was equally or more efficient in impeding the production of methional compared to the other antioxidant systems. For phenylacetaldehyde, erythorbic acid or glutathione with sulphur dioxide provided improved inhibition compared to sulphur dioxide alone, in conditions of limited oxygen consumption. The results also demonstrate the extent to which sulphur dioxide addition can lower the free aldehyde concentrations to below their aroma thresholds.     

Amperometric detection of ascorbic acid in honey using ascorbate oxidase immobilised on amberlite IRA-743

A differential amperometric method for the specific determination of ascorbic acid in honey was developed by association of a flow injection analysis (FIA) system and a tubular reactor containing the ascorbate oxidase enzyme immobilised. A gold electrode modified by electrochemical deposition of palladium was employed as working electrode. Ascorbic acid was quantified in seven samples of commercial honeys using a potential of +0.60 V vs. Ag/AgCl_(sat). The linear dynamic range in ascorbic acid extends from 1 to 50 μmol L⁻¹, at pH 7.0. At flow rate of 1.5 mL min⁻¹ and injecting 250 μL sample volumes, a sampling frequency of 180 determinations per hour is afforded. The detection and quantification limit of this method are 0.14 and 0.49 μmol L⁻¹, respectively. The samples analyses were compared with the volumetric method, and showed an excellent correlation between the methods.     

Antioxidant potential of aroma compounds obtained by limonene biotransformation of orange essential oil

The antioxidant activities of a limonene biotransformation extract and of some standard monoterpenes present in the extract were assessed using four antioxidant assays: total antioxidant capacity, based on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay, lipid peroxidation by the thiobarbituric acid (TBA) assay, superoxide anion release by cultured leukemic cells and glutathione S-transferase (GSTs) activity. The limonene biotransformation extract had free radical-scavenging activity (EC₅₀ = 2.09%, v/v) and inhibited lipid peroxidation (IC₅₀ = 0.13%, v/v). The extract, perillyl alcohol and α-terpineol inhibited lipid peroxidation by ∼80% at a concentration of 0.02% (v/v). Perillyl alcohol and α-terpineol also reduced the release of superoxide anions by cultured leukemic cells, by 3- and 10-fold, respectively, at concentrations of <0.02% (v/v). The biotransformation extract inhibited the conversion of nitrophenyl acetate to p-nitrophenol in the glutathione assay by ∼50%. These results indicate that, in addition to monoterpenes, other non-volatile compounds may contribute to the antioxidant activity of the biotransformation extract.     

Determination of ascorbic and isoascorbic acid in beverages and additives to meat products by capillary isotachophoresis

 A isotachophoretic method with conductivity detection was developed to directly determine ascorbic acid in food samples. The leading electrolyte contained hydrochloric acid (10 mmol/l), β-alanine (pH 3.0), and methylhydroxyethylcellulose (0.1%). The terminating electrolyte was 5 mmol/l caproic acid. The method is suitable for determining ascorbic acid in juice, beers, and as additives to meat products. The method was also applied for the determination of isoascorbic acid in additives to meat products. Received: 21 February 2000 / Revised version: 15 May 2000     

Stability of sorbic and ascorbic acids in packed green table olives during long-term storage as affected by different packing conditions,and its influence on quality parameters

The effect of different packing conditions on sorbate stability was studied in Spanish-type green table olives stored for up to one year. The factors studied were preservation treatment (pasteurisation vs. non-pasteurisation), storage temperature (room temperature vs refrigeration), packaging material (glass bottle vs. plastic pouch), storage time, and the presence or not of an antioxidant additive (ascorbic acid). Sorbic acid was stable in pasteurised samples as well as in the refrigerated unpasteurised samples, both in the absence and in the presence of ascorbic acid. In unpasteurised samples stored at room temperature, sorbic acid gradually disappeared, with a concomitant increase in the concentration of trans-4-hexenoic acid, which could be attributable to the action of lactic acid bacteria. Ascorbic acid was always less stable than sorbate. Sorbate addition negatively affected the colour parameters of both fruit and brine. An appreciable off-flavour was detected in the samples in which sorbate had been degraded.     

Validation of a HPLC method for simultaneous determination of main organic acids in fruits and juices

A liquid chromatographic method for fast and simultaneous determination of tartaric, malic, ascorbic and citric acids was validated for further application to fruits and juices. Moreover, the organic acids content of commercial samples of fruits and juices were evaluated, as well as the ascorbic acid stability during the storage. Determination of organic acids was carried out using a liquid chromatograph coupled to a diode array detector, with reversed phase (C₁₈ column) and isocratic elution with 0.01 mol L⁻¹ KH₂PO₄ (pH = 2.60) mobile phase. The validation parameters showed efficiency, adequate linearity, relative standard deviation values between 0.4% and 2.3% (n = 10) for repeatability and from 1.2% to 5.0% (n = 18) for reproducibility, limits of detection (LD) were between 0.03 and 3.31 μg mL⁻¹ and quantification (LQ) were between 0.10 and 11.03 μg mL⁻¹, recovery rates were between 82% and 110%, for two levels. In addition, the method is fast (10 min) and generates low and non-toxic residues. The values found for vitamin C were about 10 times above the values declared at the package. Ready to drink juices have a composition similar to the fruit, concerning to organic acids, except for the powder juice, in which only ascorbic and citric acids were found, for all tastes. After opening the package, a decrease of 14.0% and 27.0% in ascorbic acid content was observed for orange powder and ready to drink juices, respectively.     

Effect of ascorbic acid on the odours of cloudy apple juice

Ascorbic acid is used in apple juice as an antibrowning agent. This study investigated the effect of ascorbic acid (0.0–0.2% w/v) on the odours of cloudy apple juice using sensory evaluation and gas chromatography (GC). The increase in ascorbic acid concentration in the apple juice resulted in increases in green and unnatural odours and decreases in fresh, fruity and apple-like odours. In the GC determination, 23 volatile compounds were detected in apple juice. Aroma value, which showed the relative importance of volatile compounds, was used to elucidate the changes in odours of apple juice due to the addition of ascorbic acid. The aroma values of hexanal and trans-2-hexenal in the apple juice with 0.2% w/v ascorbic acid increased about 4 and 5-fold from those in the ascorbic acid-free apple juice, respectively. On the other hand, the aroma values of esters insignificantly changed in the apple juice with ascorbic acid. The increases in aroma values of aldehydes corresponded well with the increase in green odour in the apple juice with ascorbic acid.